Its most basic geometrics, so nothing to check there.
Lenses for use with medium format digital are not bigger than those for full frame, and full-frame lenses are not bigger than lenses used with crop-frame cameras.
The same was and is true for film. 35mm, medium format, large format - lenses were not necessarily bigger for each larger format.
On what planet is this generally true?
Earth, smart guy.
While it's true that crop sensor and full frame lenses are generally about the same size:
That's right. Now do the math.
a) Nikon, at least, has a line of lenses built for crop sensors which are quite light albeit not physically very small
The cheap ones have fewer elements, which makes them lighter. You can get them for full frame Nikons and Canons as well. The sensor size doesn't dictate the lens size or weight.
b) medium format lenses are often much bigger than equivalent 35mm/full-frame lenses
No, they're not. I have a couple dozen MF cameras here, and for most, I have more than one, and sometimes several lenses. You?
c) large format lenses are gigantic beasts for an equivalent.
No, they absolutely are not. I have a few of them here as well and can clearly see with my own eyeballs from where I'm sitting that they do not have gigantic beasts for lenses. You?
Lens sizes DO go up for larger formats, all else being equal.
No, they don't. I don't know where you're getting your information, but it's just not true.
What Solarflare probably means is:
make the sensor twice as wide, and it gets 4x the area (this has been covered)
Not unless you also make it twice as long. And then we're not "doubling the size" anymore; We're talking about doubling the dimensions - two very different things.
AND the equivalent lens length also doubles.
No, it absolutely doesn't.
In order to retain the same aperature, it also gets twice as wide,
The physics of larger sensors and film planes is that they don't need the same apertures as smaller ones to achieve the same DOF, look and quality.
and since it's a cylinder, twice as tall, which is in fact 8x the "size" in some sense. In reality the length only goes up a little, since you're MOSTLY just moving it further from the image plane for length. It does go up 4x in cross section, and it does get physically longer, though.
This is just silly. Go look at medium and large format cameras and their lenses, and get back to me.
I'm looking at several shelves full of DSLRs and SLRs and TLRs, crop, full, MF and LF, and I can see quite clearly that the lenses on them have NO requirement to be bigger for the larger format films/sensors. In many cases, the MFs and LFs actually have smaller lenses than the SLRs and DSLRs.
Oh, and while you're pulling balogna out of dark crevices, explain how it's at all possible for all these large format pinhole cameras to work at all, if they need "giant beasts" for lenses:
http://www.google.com/search?q=larg...w&biw=1284&bih=877&sei=PW0ZUOSXNc_siQKAyYH4BA